This study will examine how the herbal remedy ginkgo biloba may affect the body's elimination of other medicines. Many people take ginkgo biloba to improve memory, mental alertness and overall feeling of well being. Since this product is considered a food supplement and not a drug, it is not subject to the rigorous pre-market testing required for prescription and over-the-counter (OTC) drugs. As a result, information has not been collected on possible interactions between ginkgo biloba and other medications. This study will look at how ginkgo biloba affects the elimination of phenytoin-a medication used to treat patients with seizures.